Eyeglasses having exchangeable lenses offer several advantages over conventional eyeglasses having fixed lenses. For example, in the case of sunglasses, different pairs of lenses can be provided for varying light conditions. Some of these lenses are preferably polarized to protect the eyes against ultarviolet rays. In the case of prescription glasses, lenses manufactured to the current prescription of the wearer can be easily exchanged for the out-of-date prescription lenses. Also, in the case of lens and/or frame damage, a single component can be replaced more economically than purchasing an entirely new pair of eyeglasses.
Exchangeable lens eyeglasses have been known for some time but older designs have had significant shortcomings in that they are generally of complex mechanical structure making them expensive to manufacture. Other designs require substantial mutual deformation of the lens and the front component of the frame making insertion and removal of a lens cumbersome and difficult.
Recently introduced exchangeable eyeglass designs have overcome these shortcomings by making replacement of the lenses convenient. In one structure disclosed in U.S. Pat. No. 4,176,921, the eyeglass front is disclosed as being made of wire with complete rims (rims completely encompassing the lenses). Welded to the wire rims are spaced lower hooks for supporting the lenses which are inserted from above until they are embraced by the hooks. A metal lever is hinged to the bridge joining the rims and functions, when rotated downwardly to its holding position, to prevent upward movement of the lenses. Separate plastic nose pads are attached to the wire front. The eyeglasses shown in this patent have met with widespread success but they are relatively expensive due to the wire front, welded hooks, pivoted lever and plastic nose pads which must be assembled to form the completed product.
An eyeglass configuration for a front with partial rims (rims which extend about the periphery of typically only the upper portion of the lenses) includes threads which are received in grooves in the exposed edges of the lenses. The threads are fastened to one end of their associated partial rim and meet at the bridge section of the front where their remaining ends are held by the free ends of pivotal levers for tensioning the threads. A retainer clip, which is hinged to a lower bridge member, overlies the lever free ends to maintain the levers in their tensioning positions. The front used in the eyeglasses are preferably formed of metal to accommodate the wear occasioned by the use of pivoting components, to permit the attachment of hooks, and to provide adequate strength for tensioning. For further information regarding the structure and operation of these exchangeable lens eyeglasses, reference may be made to U.S. Pat. Nos. 4,176,921 and 4,523,819.